Time delay oscillator



ch 30, 1937a R. H. VAREAN TIME DELAYOSCAILLATOR 2 sheets-Sheet 2 FiledMarh 13, 19535 INVENTOR.,

RUSSELL H.' VAR/AN. BY

Patented Mar. 30, 1937vv UNITED STATi-:s PATENT emes' TIME 'DELAYoscmm'ron Russell H. Varian, San'Francisco, Calif., assignor toFarnsworth Television Incorporated, a cor- 1 poration of CaliforniaAppiication March 1a, 1935, serial No. 10,890

s claims. (on. 25o-3 6) of flight of an electron; to provide .acathode'ray -v oscillator wherein the means for deiiecting a cathode raybeam are, also the means for colu lecting the electrons in said beam; toprovide a cathode ray tube wherein the electrons are deflected by thecharge on the collecting anodes;

to provide a cathode ray tube of simple construction and which is anautomatic oscillator; to provide a cathode ray tube oscillator having aminis mum of leads associated with the oscillating circuit; and toprovide a cathode ray oscillator operating by virtueof the time elapsedduring the passage of an electron through a predeter- 25 mined path.

Other objects of my invention will be apparent or will bespeciflcallypointed out in ,the description-forming al part of this specification,but I [do not' limit myself to the embodiment of the invention hereindescribed, as various forms may be adopted within the scope of theclaims.

Referring to the drawings:

Figure 1 is a perspective view, in elevation, of a preferred form ofcathode ray tube of my invention wherein the envelope walls have beencut away to show the internal elementa t. -Figure 2 fis adiagramindicating thevarious positions of the beam during a completecycle.

Figure 3 is a diagram, reduced to lowest terms, 40 of a simple circuitin which my invention may be utilized.

Figure 4 is a perspective View similar to Figure 1, showing amodification oi.' my invention wherein the impact area oi the receivedbeamis ofi- 45 In broad terms Iof method, my invention comprisesgenerating a beam of cathode rays, defleeting said beam near the source,projectingv said beam into space, and causing said beam to .n return toa position close to the plane oi' deection, there to be collected. r Iprefer to cause the potentials produced by the collection of the beam vto deiiect the beam. Due to the time .delay ci the electron during itstravel i'romthezone of 55 deflection back to the zione ol' collection, Iam able to create an oscillating current in an external circuit. Theoperation of the tube depends upon the time delay between thedeflectionand the collection, and also [on the fact that a deiiectionvelocity received close to the: source 5 produces avmuch greaterdeiiection than an equal velocity received as the electron returns to bei collected.

In broad terms of apparatus, my invention comprises a pair of anodes andmeans for passing 1o an electron beam through an aperture between them.I then provide means -for imposing a -retarding potential on said beamto cause it to change its course and return to be collected by theanodes. The potentials imparted to the two anodes by collection of theelectrons causes deflection totake place. Proper adjustment of the timeof ight `will cause the beam to automatically oscillate from one anodeto the other.

A tuned circuit is preferably connected across the anodes. y. v

l The method and' details of construction of my vinvention may be easilygathered from the fol.

lowing description: Y Y

Referring to Figure 1, showing a preferred vform of myinvention, acylindrical envelope i is provided at one end with a reentrant stem 2. Apress 3 of this stem carries a pair of cathode leads 4l supporting alinear cathode 5. An accelerating anode 8 provided with a linear aper-30 ture 1 is held by means of accelerating anode leads 8so that the,aperture 1 is immediately over and parallel with the linear cathode 5.In Figures 1 and 4 the electrodes have been sepa-z rated more thanthey'would be in actual prac- 35 tice, this larger separation being hereshown for the sake of' clarity in illustration. This combina'- tion oflinear cathode and linear anode aperture I will produce an electron beamcollimated in such a way that the long dimension oi the beam will 40 beat right angles yto the cathode and the slot, a's described in theapplication above referred to.

Slightly above the accelerating anode I prefer to position a pair ofsemi-circular collecting an- @des 9A and 9B. These anodes are providedwith 45 opposing up-turned lips i0, are in the same plane, and arepositioned with thelips spaced slightly apa#v to form a beam slit II atright angles to the of the cathode and so Icentered as to allow thecollimated beam to pass between the two anode lips. The anodes 9A and 9Bare supported by anode leads l2 sealed through the side Iwalls of thetube. l At the other end .of the tube I prefer to mount a held formingbar Il mounted on an electrode 25 lates.

lead I5. I prefer to make this electrode of relatively small wire andmount it so that the bar will extend at right angles to-the beam slit IIbetween the anodes and parallel with the aper- 5 ture 1 and the cathode5. This comprises all the structure necessary inside the tube for theproper operation of the device.

As the structure shown in `Figure 4 is very similari to that shown inFigure 1, it utilizes the same principle of operation and the samecircuits,

it Will be described at this time.- Here the envelope lIv is providedwith the same accelerating anode 6 and linear cathode 5, with theexception that the cathode and accelerating anode assembly are oli-setslightly toward one side of the tube. The two anodes 9A and 9B in thiscase are slightly overlapped and the lips I0 are short and extend onlypart Way across the overlap, thus providing an off-center beam slit.Then, by means of a focusing electrode IS supplied by a constantpotential source Il, a small continuous bias is placed on the beamcausing it to return in a position on the anodes where it does not haveto pass over the slit II as the beam oscil- In all other respects thetwo tubes are identical, and their operation will be described later. Inboth Figures 1 and 4 I have diagrammatically indicated the path of thebeam by broken lines I'I, and theimpact area, covered by the beam as itreturns to the anodes 9A and 9B, by a dotted line I6.

A circuit in which this tube may be utilized is shown, reduced to lowestterms, in Figure 3. An inductance 20 is shunted 'by a capacity 2l toyform a tuned circuit, one end of which is connected through wire 22A tothe anode 8A, and the other end is connected through wire 23B to theanode 9B. A center tap 24 of the inductance 26 is connected by means ofwire 25 to the accelerating anode, and the two together are connected bywire 26 to a source of positive potentia12l, the negative end of whichgoes directly through wire '29 to the bar electrode I and also through aresistor 30 to the cathode E. As is quite customary in diagrams of thissort. no

source oi current is shown for the cathode E.

It is belived that the operation of the device may be more readilyunderstood by reference to the anodel 6, and through the beam slit II.The

electrons in the beam travel out toward the bar I4 against the retardingnegative potential thereon, and turn at the top of their trajectory andreturn to the plane of the 9A and 9B anodes.

It will be obvious, of'course, thatv the retarding potential shall besuch that the electrons do not quite reach ie bar I4; and that thelength of path should be adjusted either by the potential on the bar orby the physical spacing of the 7 0 bar from the anodes, in combinationwith the initial velocity of the electrons, so that the time requiredfor the beam electrons to travel the distance of their course is either1/2, 3/2, 5/2 etc. of theperiod of the oscillator.

75 At` theV instant of the iirst return of the electrons to the 9Al and9B anodes, more electrons will be bound to fall on one than on theother.

In diagram A of Figure 2 I have shown more electrons falling on 9B thanon 9A. 9B therefore acquires a negative charge and 9A an equal andopposite `positive charge. The lips of the anodes then act as deflectingplates, and the beam will be thrown to the left, as shown in diagram B.

'As soon as the returning electrons, however,

start to arrive on 9A, the anode 9A changes from positive to becomehighly negative, as shown in diagram C. This change immediately deflectsthe beamtoward 9B, but electrons are still re turningvto' 9A. Thestream, however, has been given the inclination toward 9B and as theintensity of charge rises, due to the full collec- Ation of the streamby 9A, maximum deflection is obtained in diagram C and the returningelectrons start to move back' again toward 9B. When they begin to arriveon 9B, as Shown in diagram D, 9B accumulates the negative charge whichimmediately starts the deflection in the direction of 9A, asl Shown indiagram E, and the cycle is repeated as indicated in diagram F.

As plates 9A'and 9B are connected to anY oscillating circuit theoscillationsset up therein .by the collection of the electrons will becontinuous, and all that is necessary for maximum output of sustainedoscillations is that the time of ilight be so regulated that theelectrons will fall on one plate while being deflected near the sourcetoward the other plate. The action might be compared in physical analogyto the result which would be obtained if a garden hose nozzle were heldin the hand, directing a stream of water therefrom straight in the air.A slight horizontal oscillation given to the -nozzle would cause thereturning water to land on one side or the other of the nozzle, and itwould be quite possible to reproduce the entire action with water if thewater collected could be made to oscillate the nozzle, and the time offlight of individual drops of water be properly adjusted. f

It will be noted that in the device shown in Figure 1 the returningelectrons pass directly across the slit II and intermingle with theoutgoing electrons, and that due to this fact there lwill be a slighttime gap in the output energy as some returning electrons will pass backthrough the slit. I have avoided this action in the construction shownin Figure 4 by overlapping the plates and causing the returningelectrons to .travel in a path toone side of the slit. In this mannerthere is no loss of returning electrons nor do they, except at thebendin the path, intermingle with the outgoing electrons.

While both the outgoing and returning electrons are subject, in varyingdegrees, to the deflection potentials, the deiiection velocity vreceivedas the electrons leave the accelerating anode produces a much greaterdeilection than an equal velocity received as the electrons return to acollecting anode. The displacement of the beam may thus be' accomplishedwithout difculty.

The frequency produced by the device will vary as the square root of thevoltage between the cathode 6 and the accelerating anode A, provided thebar electrode ,I4 is only slightly negative with respect to the cathode5.- If, however, the bar electrode I4 is made considerably more negativewith respect to the cathode 5, by means of a battery or otherarrangement, the frequency will vary in the reverse direction if a largedat plate is used instead of the bar I4. If, however, a eld,

due tothe electrode I I, which varies in strength directly as thedistance from the accelerating anode 6 c an be set up, the repellingforce on the electron is directly proportional to the distance 5 fromthe accelerating anode. lA ileld of this type can be closelyapproximated by the use of the narrow bar electrode as shown. Thedifference of potential between this bar and the cathode may be adjustedby means of the resistance 30 to l give the best compromise possible.

When these factors have beentaken care of, we have the law of the springpendulum fulfilled in which the resisting force is proportional to thedisplacement; and the period is independent of l the amplitude. Theseconditions would make the frequency of .the loscillator substantiallyindependent of voltage. It is not, however, necessary that this law beexactly fullled in order to make the frequency independent lof voltagesover a small range. It is entirely practical to so arrange the elds andthe potentials in the tube that the frequency will be constant over thenormal range of the line fluctuations when the potentials even- I tuatefrom converters attached to current mains. It will be apparent to allthose skilled in the art that by proper adjustment of the resistance 30,

to change the bias between the cathode 5 and -the Y bar. electrode i4,and using the proper travel distance and the proper voltage on theanodes to correspond with the frequency desired and fixed by theconstants of the tuned circuit, that ordinary line voltage fluctuationswill not change the frequency to an extent which would, in any way, .beinimical to the-practical operation of the device. If the bias on thebar Il be tied in with the potential of the anodes, some compensationwill occur. l

The uses and advantages of the invention are obvious. It would of coursebe possible to build 40 a device wherethe bea'm traversed a long tube,eventually landing on collecting anodes. Leads from these anodes,however, would have to be brought back along the 'tube to deectingplates positioned near the source. The existence of these leads wouldimmediately destroy the ability of the tube to oscillate at ultra highfrequencies and for that reason deiiecting the stream and collecting theelectrons 'therein in substantially the same plane allows such leads tobecome non-v existent, the deflecting means and collecting means beingthe same piece of metal.

To carry the application of this device to its ylogical conclusion forthe production of ultra high frequencies, the, anodes 9A and 9B may bedirectly connected to the respective ends of a L radiating dipole,thesize of which will control, in conjunction with a properly coordinatedtravel time, the frequencyof oscillation. Furthermore,

- it is easily possible to modulate this oscillator by 60 the useof agrid tocontrol the current ofthe cathode ray beam. This grid wouldeffect the amplitude of oscillation of the beam, giving a req generativeeffect on the modulation, but lt would not changel the frequency. c5 Asthe time delay b etween deflection and collection determines thefrequency, mit will be obvious the frequency varies4 as I4. AS this cultto maintain a very accurate fixed potential upon it by other means, asthis electrode d'raws no current. Other means of stabilization will alsobe apparent to those skilled in the art.

As the frequency can be changed bythedirect current .potential of barI4, it is quite obvious that the oscillator can be synchronized withother `devices utilizing the charge on the bar I4 as a frequencycontrol.

` The actual physical dimensions of a tube necessary to obtain a givenfrequency should next be considered. The velocity V of an electron:

where E is themelectrostatic voltage, C is the charge on the electron inelectrostatic volts, and

M is the mass of theelectron. .If the anode po# As D=VT where V isvelocity and T time; the

total distance travelled by an electron is 12.4 cm. The distance one wayis 6.2 cm. or 2.44 inches.

It will be seen, therefore, that the tube is entirely practical andcompact in its structure.

QA tube such as the one shown in the drawings may be operated-.at one,three or ve times the fundamental frequency, but is probably limitedpractically to the lower harmonics unless the region of deflection canbe limited to a very exn ceptionally short distance from theaccelerating anode. The shorter this distancevthe easier the tube willwork on the higher harmonics.

Since the frequency which can be handled by this tube is determined to adegree by the time spent by the electrons between the deflecting plates,and the sensitivity to deflection goes up as the total time of flight ofan electron increases, it is not advantageous toshorten the tube indenitely for excessively high frequency operation. It has been found,however, that tubes of the construction shown with practical spacingswill operate satisfactorily lbetween 30 and 200' megacycles.

It is also possible vto adapt the tube to produce much lowerfrequencies, and in case it is desired to use such lower frequencies Iprefer to put a screen grid above the anodes 9A and 9B which is negativethereto but positive tothe cathode. This will produce a long electronpath at relatively low averagevelocities, and greatly increase the tineof flight. It will be obvious that with this latter arrangement thedeflection sensitivity will also be increased. It is possible by the useof such a grid to g'o below 10 megacycles.

It is therefore seen that my invention is limited in its'production ofhigh frequency oscillating current only bythe loss of deflection`sensitivity with very short paths, and in the production of lowfrequencies only by the ability to lay out a sufficiently long path. Thelimitation on the high frequencies may be, in certain desirable cases,removed by some sacrifice of emciency, and the device may be used tosupply a small oscillating current at an extreme high frequency wheremost of the energy is needed for deflection.

The limited output may then be amplied by other means.

Within its wide range in the ultra high band,

therefore, the device is an eflicient and' what might be termed an easyoscillator. It starts at a long distance from the power supply, as onmasts. The circuit is exceptionally simple, and

the device, when attached to a di-pole, needs only' filament vand anodesupply wires with no necessity for complicated circuits. The physicaldimensions of the tube for extraordinary high frequencies may be maderelatively large; accuracy of construction may thereby be obtained. Nocritical adjustments are necessary, and the device may be readilymodulated. V

I claim: l

1. The method of producing sustained oscillations which comprisesgenerating a beam of electrons, projecting said electrons into space,returning said electrons to a plane adjacent the source, collecting theelectrons substantially in said plane, and applying the charge producedthereby in the same plane to said beam to produce deflections thereof.

2. The method of producing sustained oscillations in a cathode ray tubehaving an electron source and a pair of collecting electrodes whichcomprises positioning said `electrodes adjacent said source, directingelectrons between said elecmove said beam to cause electrons to returnto the other of said electrodes.

3. In a cathode ray tube'comprising an envelope containing a cathode andan anode, for

. producing a cathode ray beam, a pair of collectdelectors when chargedby collection.

4. In a cathode ray tube comprising an. envelope containing a. cathodeand anode adapted to produce a cathode ray beam, a pair of electrodesseparated to allow said beam to pass therebetween into space, means forreturning said beam to the plane of said electrodes for collection,

the charge imparted to said electrodes thereby acting to deflect saidbeam, means for regulating the time of flight, and means for stabilizingvelope containing a cathode and anode adapted to produce a cathode raybeam, a pair of electrodes separated to allow said beam to passtherebetween into space, means for returning said beam to the plane ofsaid electrodes for collection, the charge imparted to said electrodesthereby acting to deflect said beam, means for regulating the timev offlight, and means including a tuned circuit connecting said electrodesfor stabilizing the deflections.

6. In a cathode ray tube comprising an envelope containing a cathode and.anode adapted to produce a cathode ray beam, a pair of dual purposeelectrodes separated to allow said beam to pass therebetween positionedclose to the source of -said beam, means for producing an alternatingdeflection charge on said electrodes by collection of electrons fromsaid beam, and means for regulating the frequency of deection.

7. In a cathode ray tube comprising an envelope containing a cathodeandl anode adapted to produce a cathode ray beam, a pair of electrodesseparated to allow said beam to pass therebetween positioned close tothe source of said beam, means for producingan alternating deflectioncharge on said electrodes by collection of electrons from said beam,means for regulating the frequency of deflection, and means forutilizing the excess of electrons over the power necessary fordeflection.

8. In a cathode ray tube having an envelope containing a cathode andanode adapted to project a beam of cathode rays into space, a pair ofelectrodes positioned close to the source of said beam and separated toallow said beam to pass therebetween, meansl for returning said beam to4the plane of said electrodes, means for regulating the time of flightoi the electrons in said beam, a tuned circuit connecting saidelectrodes, and means for offsetting the beam in space so that it willdescribe a path across said electrodes during collection apart from theregion wherein electrons are passing outwardly between said electrodes.l

RUSSELL H. VARIAN..

